TJ-II: impact of impurities on turbulence

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Experimental campaign

Spring 2022

Proposal title

Impact of impurities on turbulent transport

Name and affiliation of proponent

García-Regaña, J. M., Baciero, A., Calvo, I., Carralero D., Estrada T., González-Jerez A., López-Miranda, B., Medina, F., McCarthy K. J., Ochando, M. A., Thienpondt, H., Velasco, J. L., and the TJ-II team, Laboratorio Nacional de Fusion, CIEMAT (Spain)

Details of contact person at LNF

jose.regana@ciemat.es

Description of the activity

Motivation.

In the context of analytical theory, the stabilizing role of impurities on Ion-Temperature-Gradient (ITG) driven instability has been known for decades, see e.g. [1], where the derived linear dispersion relation shows that the increase of the impurity concentration has a positive impact on the critical gradient of the toroidal ITG mode and its growth rate. Numerically, and on a quasi-linear fashion, in [2] the benign impact of increasing the effective charge, $Z_{\text{eff}}$, on ITG stability is demonstrated, albeit for the simplified slab geometry, at the time that the impact is found deleterious for Trapped Electron Modes (TEMs). The interest in these early works and on the question itself about the active role of impurities on the overall turbulence behavior has been brought to the front line of stellarator research by recent experiments in W7-X [3]. In the reported experimental conclusions, it is highlighted an increase of up to a 30% in the central ion temperature follows the injection of non-trace amounts of Boron. Given the evidence

Proposal

In the present proposal the impact of impurities on the background turbulence will be studied.

International or National funding project or entity

Include funding here (grants, national plans)

Description of required resources

Required resources:

  • Number of plasma discharges or days of operation:
  • Essential diagnostic systems:
  • Type of plasmas (heating configuration):
  • Specific requirements on wall conditioning if any:
  • External users: need a local computer account for data access: yes/no
  • Any external equipment to be integrated? Provide description and integration needs:

Preferred dates and degree of flexibility

Preferred dates: (format dd-mm-yyyy)

References

  1. R. R. Domínguez and M. N. Rosenbluth, Nuclear Fusion 29 844 (1989).
  2. R. R. Domínguez and G. M. Staebler, Nuclear Fusion 33 51 (1993).
  3. R. Lunsford et al Phys. Plasmas 28 082506 (2021)

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